A fire needs three things to ignite and continue to burn—heat, fuel and an oxidizing agent, usually oxygen. A fire can be extinguished by removing any one of these three elements. In North America, cooking oil and grease fires represent about 40% of all home fires. In some areas of Europe, the figure is even higher.
Fire departments are overloaded with paramedic calls; the typical response time in North America for a fire is more than 8 minutes, during which time a cooking oil fire can do tremendous damage or spread out of control. Clearly, families need a way to extinguish a cooking oil fire on their own, quickly and safely.
Portable, chemical fire extinguishers are believed by many homeowners to be a panacea for all types of fires. Not so. Recent changes to cooking methods have brought new safety risks to the use of portable, chemical fire extinguishers. The replacement of animal fats used as cooking oils with healthier vegetable oils has reduced the ability of dry chemical fire extinguishers to effectively put out cooking oil fires. Vegetable oils have lower fatty acid content, which prevents the dry chemical's intended “foam blanket” from developing and inhibits the extinguishing agent by allowing vapors and steam to release. Additionally, vegetable oils have a much higher auto-ignition temperature than animal fats, so some newer fryers are designed to operate at higher temperatures. These ‘energy-efficient’ fryers retain heat much longer than previous models. Portable, dry chemical fire extinguishers have trouble preventing a re-flash from occurring in these new fryers, because of the large amount of retained heat. Heat breaks down the “foam blanket”, meaning that the fire may keep self-igniting until the oil cools down.
There are several other drawbacks to the untrained homeowner attempting to put out a cooking oil fire with a portable chemical fire extinguisher:                a) There are 4 main classes of portable chemical fire extinguishers. Using the wrong kind—for example, a Class A, B, or C fire extinguisher—on a cooking oil fire, will either be ineffective or will make the situation worse, threatening the safety of the family members and risking the loss of the home. Most homeowners do not know that only Class K fire extinguishers can be used on a cooking oil fire.        b) Most homeowners do not hang their portable chemical fire extinguisher in the kitchen, because they do not feel the devices are attractive. This means the fire extinguisher will not be instantly deployable. Some homeowners may even forget where they stored their fire extinguisher, which will cause lost time in the event of a fire.        c) Portable chemical fire extinguishers need recharging. Most homeowners do not track when their fire extinguisher needs recharging. An out-of-date chemical fire extinguisher may be of no help.        d) If the homeowner should have a Class K fire extinguisher, and if he remembers where he put it and finds it quickly, and if the fire extinguisher has been appropriately recharged, there is still a huge problem—lack of training. Most homeowners purchase their fire extinguishers from mass merchants and, therefore, are not trained in the proper use of their device, especially on something as dangerous as a cooking oil fire. There is an appropriate distance that the user must stand from the fire and an appropriate place to aim the fire extinguisher. The chemical can exit the fire extinguisher nozzle with significant force. A high-powered stream aimed directly at the burning oil can cause it to splash, spreading the fire throughout the kitchen and onto the carpet. Standing too close to the burning oil while using a chemical fire extinguisher can cause life threatening burns.        e) Portable chemical fire extinguishers with plastic parts have proven to be unreliable or defective. One manufacturer recently announced the recall of 37 million fire extinguishers in the United States.        f) Portable chemical fire extinguishers have the disadvantage that, upon use, the entire kitchen will be contaminated and will require a significant, sometimes expensive, clean-up effort. Class K fire extinguishers contain saponifiers—alkaline mixtures such as potassium acetate, potassium citrate, or potassium carbonate. The alkaline mixture combines with the fatty acids in cooking oil to create a soapy foam layer on the surface of the vessel, which is intended to hold in the vapors and steam. Eventually, if the entire burning vessel has been appropriately sprayed, the fire will be extinguished. Unfortunately, the process also creates quite a mess in the kitchen.        
Fire suppression blankets are used in many countries in Europe and other parts of the world to attempt to extinguish cooking oil fires, the concept being to cut off the supply of oxygen to the fire. However, fire suppression blankets also have some significant disadvantages. Current commercially available fire suppression blankets are often stored in the home, still in the manufacturer's packaging, neatly folded. This means the blanket will not be instantly deployable, which can cause lost time in the event of a fire. After the blanket is opened, simply throwing the blanket on a cooking oil fire is not a good idea. A missed throw may cause the pan to splash burning oil on the user and/or all over the kitchen, resulting in burns to the user and the fire spreading out of control. Attempting to get close enough to be able to slowly and carefully cover the fire with the blanket is not practical. A cooking oil fire is simply too hot to get sufficiently close to it. Further problems will result if a corner of the blanket lands in the cooking oil. Instead of eliminating the supply of oxygen and putting out the fire, the blanket material will act as a wick and start to burn.
United States Patent Application Publication US 2007/0158084 A1 (Schwartz) discloses a Deployable Fire Extinguishing Towel, comprising a deployable flexible frame and a fire resistant material mounted to the flexible frame for being applied on a fire for extinguishment thereof. To the frame is mounted a handle which allows the user to place the fire resistant material over the burning object, such as a pan. This Fire Extinguishing Towel has several drawbacks. The handle is rigidly mounted to the frame but, in the depicted embodiment, is too short to allow the user to remain a safe distance away from the fire. The requirement that the frame be flexible enough to change shape when placed in the storage container, is counterproductive, resulting in a device in which the flexibility of the frame does not allow the fire resistant material to create an adequately airtight seal when covering the cooking vessel. The lack of an adequate airtight seal allows the oil fire in the cooking vessel to continue to burn. The springs used for automatic deployment are under load in the storage position and therefore will gradually lose their strength or become out of round, no longer providing a flat surface to effectively cover the pan, thereby not creating an airtight seal and not cutting off the supply of oxygen and allowing the fire to continue to burn.
U.S. Pat. No. 5,842,525 (Graham) discloses a burning pan fire extinguisher where the fire extinguishing material is supported and automatically extended by folding arms which are made, for instance, of helical springs. The folding arms are attached on opposite sides of a frame which supports the folding arms and extend across the fire extinguishing material in all positions of use. From the frame extends a short handle which is made to fold for compact storage by pivoting with respect to the frame through 180 degrees. This fire extinguisher also has several drawbacks. The folding arm springs are under load in the storage position and will lose their resiliency during the long periods of time the device is typically in the storage position. This may cause a malfunction of the device during its opening into the usage position. The handle is a flat resilient plate which is difficult to handle and is too short to permit the user to remain a safe distance from the fire. The frame obstructs proper covering of the cooking vessel. The resiliency of the folding arms makes covering the cooking vessel difficult. The preferred embodiment depicts a helical spring, flexible enough to be twisted into the shape of a figure eight when put into storage. This degree of flexibility will be counterproductive when trying to put out a cooking oil fire, since the flexibility prevents sufficient downward pressure from being applied by the user to tightly cover the cooking vessel on fire.
Both Schwartz and Graham teach the use of springs that are under constant load while the devices are in storage. Neither Schwartz nor Graham has sufficiently taken into consideration the material properties of springs and the effect that gradual plastic deformation will have when the springs are under constant load for long periods of time. When purchasing a fire extinguishing device, the homeowner is purchasing a safety device that may not be needed for several years, during which time it will be in the storage position. If the spring is under constant load, that is, displaced from its equilibrium position, a very slow plastic deformation will gradually take place. This is referred to as creep when the spring under constant load loses length, ie. fails to return to its equilibrium length. When the spring under constant compression loses load, it is referred to as relaxation, ie. the spring weakens. Since the springs in both Schwartz and Graham are under constant compression in the storage position, the creep/relaxation properties of springs will cause these fire extinguishing devices to eventually fail after being in storage for a long time. In this case, unfortunately, in the event of a fire, the homeowner will simply realize that the device does not work.